Chemistry - Chemical Thermodynamics
EXPLAIN TO YOURSELF.
When a chemical reaction happens, an energy change occurs. The
energy change may appear in different forms:
1. Heat and light: Energy change involved in combustion of fuels
like kerosene, coal, wood, natural gas is in form of heat and light.
2. Electrical energy: Example: chemical reactions in batteries.
3. Light energy absorption: formation of glucose (C₆H₁₂O₆) during
photosynthesis using energy from the sun.
In chemical thermodynamics, we study reactions in which heat is
either evolved or absorbed.
SOME COMMONLY USED TERMS:
System and Surroundings: If we study the
reaction of two substances A and B kept
together in same beaker, The reaction
mixture of A and B together is the system.
The beaker and the room where it is kept are
the surroundings.
System: The part of the physical universe which is under study.
Surroundings: The rest of the universe other than the system.
Isolated System : Example: Hot tea/milk kept in a thermos flask remains
hot for a long time only If the flask is made of perfect insulating material,
there is no exchange of matter or energy with surroundings, hence why it
remains hot.
Isolated system: A system that cannot exchange matter or energy
with its surroundings.
Closed System : Example: Hot tea/milk in a stoppered stainless steel flask
does not remain hot after some time as Energy is exchanged with
surroundings of steel flask, Matter is not lost due to the stopper.
Closed system: A system which can exchange energy but not matter
with the surroundings.
Open System : Example: If a stainless steel flask or thermos flask is open, Matter is lost
due to evaporation and Energy is also lost. Plants, animals, and human beings are examples
of open systems.
Open system: A system which can exchange both energy and matter with the
surroundings.
, State of a System
The state of a system is described by its measurable properties.
o Example: For a gas, state can be described by pressure (P), volume
(V), temperature (T), etc.
These measurable properties are called state variables or state functions.
o Their values depend only on the initial and final state of the system.
o They do not depend on the path taken during the change.
Example: If a system changes from initial state to final state via paths I,
II, or III: Differences like change in pressure (p2-p1) and change in temp
(t2-t1) are the same for all paths. Pressure and temperature are therefore
state functions.
State functions are those functions which depend only on the state
of the system
Change in state is defined by giving the initial and final state of the system. Ex:We
travel from one point to another. The distance travelled depends on the path or the route
we take. But the separation between these two points on the earth is fixed. Thus,
separation is a state function, but not the distance travelled.
Properties of a System : As stated earlier, the measurable properties of a system are called
state variables. They’re divided into 2 types.
1.Extensive Property (variable) – is the property where it depends upon the size of the
system. For example, volume, weight, heat, etc. (here size means amount of matter/material
in system)
2. Intensive Property (variable) – is the property where it doesn’t depend on the size of the
system. For example, temperature, pressure, refractive index, viscosity, density, surface
tension, etc.
An extensive property can become intensive by specifying per unit amount. For
example, mass and volume are extensive properties, but density (mass per unit volume)
and specific volume (volume per unit mass) are intensive properties.
Types of Processes: The method of bringing about a change in state is called process. Ex:
Raising the temperature of a system by heating → heating is the process.
Types of Processes : 1. Isothermal Process – A process in which the temperature of the
system doesn’t change throughout and Even when heat is added or removed, it is fully used to
do work or cause a change of state, so the temperature does not change. Example: Ice melting at
273 K and 1 atm.
2.Adiabatic Process – In this process there is no exchange of heat between
the system and the surroundings. Thus there’s always a change in
temperature.
Example: Mixing an acid and a base in a closed thermos flask, where heat
is retained as no heat exchange.
EXPLAIN TO YOURSELF.
When a chemical reaction happens, an energy change occurs. The
energy change may appear in different forms:
1. Heat and light: Energy change involved in combustion of fuels
like kerosene, coal, wood, natural gas is in form of heat and light.
2. Electrical energy: Example: chemical reactions in batteries.
3. Light energy absorption: formation of glucose (C₆H₁₂O₆) during
photosynthesis using energy from the sun.
In chemical thermodynamics, we study reactions in which heat is
either evolved or absorbed.
SOME COMMONLY USED TERMS:
System and Surroundings: If we study the
reaction of two substances A and B kept
together in same beaker, The reaction
mixture of A and B together is the system.
The beaker and the room where it is kept are
the surroundings.
System: The part of the physical universe which is under study.
Surroundings: The rest of the universe other than the system.
Isolated System : Example: Hot tea/milk kept in a thermos flask remains
hot for a long time only If the flask is made of perfect insulating material,
there is no exchange of matter or energy with surroundings, hence why it
remains hot.
Isolated system: A system that cannot exchange matter or energy
with its surroundings.
Closed System : Example: Hot tea/milk in a stoppered stainless steel flask
does not remain hot after some time as Energy is exchanged with
surroundings of steel flask, Matter is not lost due to the stopper.
Closed system: A system which can exchange energy but not matter
with the surroundings.
Open System : Example: If a stainless steel flask or thermos flask is open, Matter is lost
due to evaporation and Energy is also lost. Plants, animals, and human beings are examples
of open systems.
Open system: A system which can exchange both energy and matter with the
surroundings.
, State of a System
The state of a system is described by its measurable properties.
o Example: For a gas, state can be described by pressure (P), volume
(V), temperature (T), etc.
These measurable properties are called state variables or state functions.
o Their values depend only on the initial and final state of the system.
o They do not depend on the path taken during the change.
Example: If a system changes from initial state to final state via paths I,
II, or III: Differences like change in pressure (p2-p1) and change in temp
(t2-t1) are the same for all paths. Pressure and temperature are therefore
state functions.
State functions are those functions which depend only on the state
of the system
Change in state is defined by giving the initial and final state of the system. Ex:We
travel from one point to another. The distance travelled depends on the path or the route
we take. But the separation between these two points on the earth is fixed. Thus,
separation is a state function, but not the distance travelled.
Properties of a System : As stated earlier, the measurable properties of a system are called
state variables. They’re divided into 2 types.
1.Extensive Property (variable) – is the property where it depends upon the size of the
system. For example, volume, weight, heat, etc. (here size means amount of matter/material
in system)
2. Intensive Property (variable) – is the property where it doesn’t depend on the size of the
system. For example, temperature, pressure, refractive index, viscosity, density, surface
tension, etc.
An extensive property can become intensive by specifying per unit amount. For
example, mass and volume are extensive properties, but density (mass per unit volume)
and specific volume (volume per unit mass) are intensive properties.
Types of Processes: The method of bringing about a change in state is called process. Ex:
Raising the temperature of a system by heating → heating is the process.
Types of Processes : 1. Isothermal Process – A process in which the temperature of the
system doesn’t change throughout and Even when heat is added or removed, it is fully used to
do work or cause a change of state, so the temperature does not change. Example: Ice melting at
273 K and 1 atm.
2.Adiabatic Process – In this process there is no exchange of heat between
the system and the surroundings. Thus there’s always a change in
temperature.
Example: Mixing an acid and a base in a closed thermos flask, where heat
is retained as no heat exchange.
